A few years ago I did a DIY resto on my 1914 Farm Victorian. I took out the lathe and plaster and replaced with 1/2 or 5/8 (can't remember)sheet rock. When I put the original trim back up, I had a very noticeable gap between the door casing and the dry wall. Or between the casing and the jamb. Unfortunately I left the gap.
Now I'm on to my second house which is 3 times the size of the previously mentioned house and 3 times as much trim; entry way's columns, casings, base, etc... I'm looking at doing a complete gut like before but this time I actually want the trim and dry wall to sit flush with each other so it actually looks professional! What would be the best way to achieve this?